The intracellular concentration of oxygen is important to a host of physiological and pathological functions, yet can be a difficult variable to quantify. The use of EPR oximetry to study intracellular oxygen concentration is being refined and applied by Prof. Swartz and co-workers to studies of cultured cell lines, indicating that significant differences in this parameter between extra and intracellular compartments exist and can be accurately and reproducibly measured. Current research is focused upon: improving the signal to noise ratio of the resultant EPR spectra, improving the stability of cell preparations to allow study of pharmacological modulation of intracellular oxygen, and complimentary theoretical approaches to the modeling of intracellular oxygen concentrations. Complimentary fluorescence-based approaches to this study are being developed in collaboration with Dr Dobrucki.